Question

bromine is a red-orange liquid with an average atomic mass of 79.90. its name is derived from the greek word ""bromos"" meaning ""stench"". it has 2 naturally occurring isotopes: br 79 (78.92 amu) and br 81 (80.92 amu). what is the % abundance of the heavier isotope?

Answer 1

the heavier isotope is Br-81.

to find the percentage abundance, you can use the following equation:

(exact weight of isotope #1) (abundance of isotope #1) + (exact weight of isotope #2) (abundance of isotope #2) = average atomic weight of the element

so we plug in the values, where x is our percentage abundance

(78.92) (x) + (80.92) (1 - x) = 79.90

we solve for x.

78.92X + 80.92 - 80.92X= 79.90

78.92X - 80.92X = 79.90 - 80.92

-2X= -1.02

X= -1.02 / -2= 0.51 or 51%

51% represents the abundances of the lighters isotope. to find the heaviest, we just subtract 100 to it. 100-51= 49 %